Construction Team Treads Lightly Around Moscone Convention-Goers

At the $500-million Moscone Center Expansion site in San Francisco, crews are racing to complete a major component of the project’s second phase—the east half of the Moscone South building. Meanwhile, demolition is just beginning on a portion of the old Moscone South building to make way for Phase 3, which, among other things, will entail building the western half of the new structure.

In order to ensure the first building half is code-compliant in earthquake-prone San Francisco so it can host conferences and conventions, engineers created an interim structural system relying upon buckling restrained braces (BRB) that will be removed once the other half of the building has been built and tied in. The project team is also weaving in an innovative water recycling scheme into the revamped center.

It’s a delicate and complex construction dance made even more difficult by the fact that Moscone Center remains operational throughout the expansion, which wraps up in late 2018.

It’s a delicate and complex construction dance made even more difficult by the fact that Moscone Center remains operational throughout the expansion, which wraps up in late 2018.

“The single biggest learning curve for us on this project was learning to work while the facility was operational,” says Spencer Reiner, Webcor Builders’ project director. “There are paying clients using the facility, and you can imagine any disruption—be it noise, vibration, dust—has an impact [on] their show.”

To keep Moscone and its $2-billion annual contribution to the local economy chugging along, the expansion was broken into several phases. Moscone’s owner, the city and county of San Francisco, brought Webcor on during the late schematic design phase in 2012 to work with architects SOM and Mark Cavagnero Associates Architects on sequencing and planning.

According to Keith Boswell, partner with SOM, the expansion will maximize the available footprint, create light-filled interior public spaces and boost the facility’s connection to the surrounding urban fabric using pedestrian-friendly spaces, outdoor terraces and a more open and transparent facade.

The team began a “make-ready” phase in fall 2014 to prep critical systems and infrastructure on the campus-like collection of buildings, such as relocating an electrical substation and moving a truck load-in ramp.

During Phase 2, begun in December 2015, crews demolished an existing lobby and administrative building on the corner of 3rd and Howard streets and built half of the rectangular Moscone South building. That phase wraps up in September. Once the west half is completed during Phase 3, which began in April, the 94-ft-tall building will be 540 ft long by 190 ft wide.

Most of Moscone’s existing exhibit space lies underground, with sprawling 1980s-era halls situated just south and north of Howard Street. But only a sliver-like connecting hall passed below the street to connect the two areas. Phase 2 of the expansion removes the plug of earth underneath the street that separated the two exhibit areas, creating more than 509,000 sq ft of contiguous space. After removing around 18,000 cu yds of earth, crews are creating a below-grade reinforced concrete post-tensioned bridge structure to carry the traffic loads on Howard Street—a major city artery.

Interim Braces

Moscone South includes three levels above grade and one level below. Like most of the new construction at the center, Moscone South utilizes an existing 6-ft to 8-ft-thick mat foundation built in the 1980s in part to provide dead-load resistance to high groundwater pressure, according to SOM.

The superstructure’s lateral system will utilize BRBs in the east and west extremes at the building core locations. Because of the building’s 37-ft floor-to-floor height and nearly 40-ft bays at the ballroom level (Level 2), the project required supersized BRBs.

“At the time of its fabrication, one of the BRBs designed and fabricated by Core Brace was the heaviest BRB that they had ever built, weighing in at nearly 15.5 tons,” says Lindsay Hu, associate with SOM, which also served as the lead structural engineer. It was also one of the supplier’s longest braces, at approximately 50 ft.

“In order to accommodate the phased construction and avoid a very eccentric core and structural system, we came up with an interim structural steel BRB system,” Hu says. As part of the system, interim gravity beams were upturned and installed above the slab, with the framing that will cross the interface between Phases 2 and 3 hung from the upturned beams. Once Phase 3 is built, the permanent members will be spliced together and the interim framing above the slab will be unbolted and removed, according to an SOM report.

By arranging most columns at the perimeter of the building, SOM created a column-free, 367-ft-long by 136-ft-wide ballroom on the second level, and other wide-span meeting rooms on Level 3. The structural gravity system features concrete fill over a metal deck, with long-spanning composite structural steel Pratt trusses and structural steel columns, Hu says.

Phase 3 will add a new skybridge on the second level between Moscone South and the existing Moscone North building, and replace a public pedestrian bridge on the extreme west edge of the property where it meets Yerba Buena Gardens.

Water Brokers

Ever since Moscone’s underground exhibit spaces were built, pumps have been sending large amounts of groundwater into city sewers. This dewatering is required for Moscone and many other downtown structures “so that the buildings don’t bubble up and out of the ground,” says Charles Chaloeicheep, senior associate with MEP engineer WSP. With the expansion, a new storage and treatment system will capture and reclaim these dewatering spoils, along with rainwater and condensate, to meet all toilet flushing and irrigation demands of the project. Water will also be used to irrigate the neighboring Yerba Buena Gardens.

Since the reclaimed water source is more than enough to meet these localized demands, Chaloeicheep says collaboration between multiple city departments hatched a plan to build a water-filling station at Moscone that will top off the city’s street-sweeping trucks. “It is estimated that the system will save over 5 million gallons of water and enable the project to achieve net positive water. It’s an amazing feat for any sized building, and it isn’t enabled by technology, but by partnerships within the local community,” he adds.

Coupled with other sustainable strategies, including an expanded solar array that will supply up to 20% of the building’s energy demand, the project team is targeting LEED platinum and net-zero carbon. Smart meters will also allow Moscone to generate detailed reports for conference organizers to track exactly how much energy, waste or water their event consumes.

Colaborative Safety

A new Webcor safety initiative makes “everybody a lifeguard” on the project, says Reiner. A smartphone app enables everyone from apprentices to managers to report near misses and incidents or to provide recognition. “We want to make it a positive environment. You don’t always want to penalize for safety,” he adds.

But safety concerns extend beyond the construction employees. Since the average exhibition move-in places 1,000 tons of exhibits in just a few days, “we saw there was a real need to have the facility also embrace our safety culture,” Reiner says. A monthly executive safety committee comprised of Webcor safety staff and facility union leaders reviews and implements safety measures. “We’ve already seen change,” he says.

This collaborative effort extends to construction coordination as well. Both Webcor and the building operator have dedicated individuals that serve as client liaisons. “In advance of every convention, the two of them meet with the convention clients in preparation of understanding the needs of the client and our needs as a builder and what [work] we are specifically doing,” Reiner says.

Temporary partitions with sound blankets, multiple layers of drywall and insulation mitigate most sound transmission from construction zones to operational exhibit space even when crews are working mere feet away from conference-goers and exhibitors.